Study On Energy Performance And Climate Suitability Of External Venetian Blind Shading For Nearly Zero Energy Residential Buildings

With technological progress and social development,research on nearly zero energy buildings(NZEBs)is an inevitable trend to achieve building energy efficiency and emission reduction.The external venetian blinds shading(EVBS)is one of the effective passive energy-saving technologies for NZEBs to improve the overall performance,which is worthy to be further analyzed and discussed.However,there is currently a lack of refined,systematic and regional research on NZEBs with EVBS.The main problems are: the existing standards lack quantification studies of EVBS to guide its regional applications;the climate suitability calculation model and the comprehensive evaluation model of EVBS for NZEBs have not yet been established;most of the existing researches are concentrated in cooling-dominant regions and there is a lack of field comparison test study;the key factors and its weights that affecting the shading effect of NZEBs have not been determined;the existing theoretical model of EVBS without considering the impact of the installation distance,which is inconsistent with the actual situation;etc.Therefore,this paper adopts five methods,including theoretical research,field comparison test,numerical simulation,sensitivity and regression analysis,and comprehensive evaluation,to comprehensively explore the energy characteristics and the climate suitability of EVBS for residential NZEBs in China.This study mainly includes the following six parts:First,according to the EVBS theory,a model for the reverse direct solar radiation of the EVBS is built with considering the impact of installation distance.Compared with the original model,the maximum difference between the total reverse direct transmittance ratio of these two models under diverse blind reflectivity,installation space to width ration,and blind space to width ratio is 2.9%,and the accuracy of the original model can be increased by up to 4%when considering the installation distance.Second,the field comparison test in cold regions is conducted to comprehensively analyze the shading performance of EVBS for NZEB.Results show that the EVBS can not only reduce the transmitted solar radiation,but also reduce the heat transfer between indoor and outdoor.During the test period,the indoor temperature fluctuation of NZEBs is less than 2?,but the maximum temperature drops by appling the EVBS can reach 0.8?,and the building cooling demand can be reduced by 13%-22%.And the illuminance reduction factor under one certain slat angle is a constant.However,when the shading slat angle is small,due to the excessive reduction of the indoor background luminance,the application of EVBS will increase indoor uncomfortable glare risk.Third,according to EnergyPlus simulation,the energy-saving performance of EVBS in different climate regions of China is analyzed and quantified.And the shading energy efficiency index SEEI is proposed to evaluate the coupling relationship between the EVBS and the envelopes of NZEBs.Results show that the energy-saving potential of EVBS for NZEBs in different climate zones is significant,especially in the high-irradiation zone up to 74%.The shading performance per unit window area of west shading is the largest,followed by east shading,south shading and north shading.And the energy-saving potential of single-orientation shading increases slowly and then rapidly increases with the increase of the slat angle in the range of 0°?180°.When the west and east window-to-wall ratio(WWR)are small,the energy-saving potential of multi-orientation shading is approximately the sum of the energy-saving potential of each single-orientation shading,and total energy-saving potential prediction of EVBS for benchmark NZEBs in different climate zones is provided.In addition,when coupling analysis of the effect of EVBS on cooling demand and daylighting according to Daysim simulation,due to the significant impact on daylighting,the energy-saving potential of EVBS is greatly reduced.As the slat angle increases,the daylighting power consumption of the EVBS is reduced.And the greater the EER of the cooling system,the smaller the comprehensive energy-saving(electricity)potential of EVBS.On this basis,the recommendation table of optimal slat angle with the largest comprehensive power-saving potential of the EVBS is provided.Fourth,the MC-AHP method is proposed,and the sensitivity analysis of relevant parameters affecting shading performance of NZEBs is performed to identify the key factors and their sensitivity ranks.Then,the regression models between key influencing factors and shading effect are established to predict the energy-saving performance of EVBS for NZEBs.Sensitivity analysis results show that meteorological parameters are the most influencial factor for cooling load of NZEBs,with a comprehensive weight of 0.82,followed by building parameters and shading parameters.Their key influencing sub-factors are temperature and solar radiation,shape factor and the south WWR,shading orientation and slat angle,respectively.On this basis,some suggestions of the optimal design of EVBS parameters for energy efficiency of NZEBs in different climate zones are provided.Regression analysis results show that the WWR,shape factor and slat angle are linearly related to the shading effect of EVBS.And the linear relationship between the EVBS performance and slat angle does not vary with the change of meteorological parameters,WWR and shape factor.Moreover,a climate coefficient table for estimating the energy-saving performance of EVBS in different climate zones is summarized.Fifth,based on EVBS theory,the effect of EVBS is divided into two parts: the solar radiation transmission reduction part and the heat transfer reduction part.Therefore,an energysaving potential formula of EVBS is established for different type of buildings,and the value tables of all unknown parameters in the formula to predict the energy-saving potential of EVBS for NZEBs in different climate regions are provided.Finally,the energy demand,lighting power consumption,environmental friendliness,and economic applicability of EVBS in different climate zones are analyzed.Based on entropy method,the comprehensive evaluation model of climatic suitability for EVBS of NZEBs is established.And the scheme optimization table of EVBS applications for NZEBs in different climate zones is provided.In addition,when discussing the carbon emission reduction(equivalent to the net electricity saving)of EVBS,a recommended table of optimal shading schemes with the best environmental benefits is provided;When discussing the lighting power consumption of EVBS,combined with consideration of the net electricity saving,the suggestions for shading application are provided;When discussing the economic applicability of EVBS,by comparing with the market unit price,the suggestions for choosing the optimal shading schemes are provided.